This section provides background information related to the present disclosure which is not necessarily prior art.
Automobile manufacturers and the entire transportation sector are facing an increasingly stringent set of governmental regulations. For example, mandates for ever lower pollutant emissions levels, as well as ever higher fuel efficiency requirements (now often expressed as ever lower carbon dioxide emissions levels) are constantly tightening. However, automobile systems which have been used successfully in the past are proving to be no longer adequate for automakers in this new environment. Therefore, to meet the new laws, mandates and requirements, automakers must adopt new technologies and systems and/or modify existing technologies and systems.
One of the automotive systems which affects both fuel economy and pollutant emissions levels is the exhaust system. Automotive engineers are discovering new ways for the exhaust system to help meet governmental mandates in these areas. For example, heat from the engine exhaust can be recovered and be used to warm the vehicle's working fluids (e.g. engine, transmission, and transaxle oil) under start-up and cold operating conditions to reduce friction, thus improving efficiency and increasing fuel economy. Improved warm-up of the engine coolant is also desirable for driver and passenger comfort because this can be used to warm up the vehicle cabin more rapidly and defrost the windshield in less time in cold start-up conditions. And because of new engine technologies, certain new exhaust components such as lean NOx traps are included in some exhaust systems to reduce smog generating nitrous oxides. These emissions components often require careful thermal regulation to maintain peak efficiency; otherwise large additions of expensive precious metals would be required to maintain conversion efficiency.
For these reasons and more, automakers are considering the addition of non-standard exhaust system components to their vehicles to achieve their goals. Specifically, controlling the flow and routing of exhaust gases to achieve thermal goals is becoming a new requirement. Heat exchangers and exhaust valves to control the flow of gases in the exhaust system are enablers for new exhaust system designs. Heat exchangers in exhaust systems can also be used, for example, to recover heat which would otherwise be lost through the tailpipe, and used in other forms to boost the overall efficiency of the vehicle systems. An example of this would be the generation of steam from the waste exhaust gas energy, which is then used to generate electricity or converted into motive power for direct vehicle propulsion.
It is often the case that the function of the exhaust gas heat exchanger is not required for the entire time that the engine is running, and therefore may require a shutoff function; likewise, the level of heat exchange may need to be controlled to a certain level below 100% of function. In cases like these, some method of controlling exhaust flow through the heat exchanger may be required. An exhaust valve is a typical technology which is used to achieve this control, as it is usually not practical to control the flow of coolant through the heat exchanger when it forms part of the engine cooling system.
Many modern gasoline engines can achieve exhaust gas temperatures between 950° C. and 1050° C. Most of today's exhaust valve designs reflect the extreme thermal environment in which this component spends its service life. While there are many types of exhaust valves, expensive, temperature-resistant materials are invariably used, and designs can be relatively complex for manufacturing. Additionally, if the exhaust valve conducts high temperatures externally, the valve's actuator may require shielding or the use of more expensive, high temperature materials.
The present disclosure provides a low-cost exhaust valve that is actively cooled by a working fluid, which may be the same fluid that flows through an associated heat exchanger. The valve does not experience the temperatures typically endured by other exhaust valves, therefore allowing for cheaper component materials having less complicated and lighter weight designs.